Sheet feeding device and image forming apparatus

ABSTRACT

The sheet feeding device includes a feed roller, a separation pad and a guide part. The feed roller is configured to feed a sheet by being rotated while coming into pressure contact with the sheet. The separation pad is configured to form a separation nip by being in pressure contact with the feed roller and to separate the fed sheet at the separation nip. The guide part is configured to guide a leading edge of the sheet to the separation nip. The apex part is formed along a feeding direction of the sheet on both outer sides of the feed roller in a width direction perpendicular to the feeding direction. The apex part projects in a direction closer to the feed roller than an extension line of the separation nip between a pressure contact position of the feed roller and the sheet and the separation nip.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent application No. 2016-136065 filed on Jul. 8, 2016, which is incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a sheet feeding device configured to feed a sheet and to an image forming apparatus including the sheet feeding device.

An image forming apparatus, such as a copying machine and a printer, includes a sheet feeding device configured to feed a sheet stacked on a sheet feeding cassette or a manual tray to an image forming part. The sheet feeding device is often provided with a separation pad configured to come in pressure contact with a feed roller in order to prevent double feeding.

If a plurality of sheets are fed, when the fed sheets passes through a separation nip formed between the feed roller and the separation pad, the sheets are separated one by one by resistance of the separation pad, and then conveyed.

By the way, when a diameter of the feed roller is reduced to save a space of the image forming apparatus, if the feed roller is used both to feed the sheet from the sheet feeding cassette and to separate the sheet at the separation nip, the following problems may occur.

That is, as shown in FIG. 8, with regarding an angle between a sheet feeding path L1 at a contact position between the feed roller and the sheet (a path in a direction of a tangential line of the feed roller at the contact position) and a sheet conveying path L2 at the separation nip, an angle β in the case of a smaller diameter feed roller R2 is smaller than an angle α in a case of a larger diameter feed roller R1. Then, the sheet is fed by the feed roller so as to collide with the separation pad and may come into contact with the separation pad on an upstream side of the separation nip without being directly fed to the separation nip.

In other words, a conveying angle of the fed sheet varies larger significantly when the sheet is fed by the smaller diameter feed roller R2 as compared to the larger diameter feed roller R1. A sheet having weak stiffness is fed to the separation nip along the separation pad because its posture can be changed corresponding to the conveying angle. However, because it is difficult for a thick sheet having strong stiffness to change its posture corresponding to the conveying angle, there is a possibility of causing conveying failure owing to resistance with the separation pad when the thick sheet comes into contact with the separation pad.

SUMMARY

In accordance with an aspect of the present disclosure, a sheet feeding device includes a feed roller, a separation pad and a guide part. The feed roller is configured to feed a sheet by being rotated while coming into pressure contact with the sheet. The separation pad is configured to form a separation nip by being in pressure contact with the feed roller and to separate the fed sheet one by one at the separation nip. The guide part is formed along a feeding direction of the sheet on both outer sides of the feed roller in a width direction perpendicular to the feeding direction. The guide part has an apex part configured to guide a leading edge of the sheet to the separation nip. The apex part projects in a direction closer to the feed roller than an extension line of the separation nip between a pressure contact position of the feed roller and the sheet and the separation nip.

In accordance with an aspect of the present disclosure, an image forming apparatus includes the sheet feeding described above and an image forming part configured to form an image on a sheet fed by the sheet feeding device.

The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present disclosure is shown byway of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically showing an inner structure of a printer according to one embodiment of the present disclosure.

FIG. 2 is a perspective view showing a feed roller of a sheet feeding device according to one embodiment of the present disclosure.

FIG. 3 is a perspective view showing a sheet feeding unit of the sheet feeding device according to one embodiment of the present disclosure.

FIG. 4 is a perspective view showing an upright part of the sheet feeding device according to one embodiment of the present disclosure.

FIG. 5 is a sectional side view showing a circumference of the feed roller in the sheet feeding device according to one embodiment of the present disclosure.

FIG. 6 is a sectional side view showing a guide rib in the sheet feeding device according to one embodiment of the present disclosure.

FIG. 7 is a view showing a thin sheet deflected between the pair of guide ribs in the sheet feeding device according to one embodiment of the present disclosure.

FIG. 8 is a view showing variations in a conveying angle caused by feed rollers having different diameters.

DETAILED DESCRIPTION

Hereinafter, with reference to the attached drawings, an image forming apparatus and a sheet feeding device according to one embodiment of the present disclosure will be described.

With reference to FIG. 1, an entire structure of a printer 1 as the image forming apparatus will be described. FIG. 1 is a side view schematically showing an inner structure of the printer 1 according to one embodiment of the present disclosure. In the following description, a near side of a paper plan of FIG. 1 is defined to be a front side of the printer 1, and right and left directions are defined based on the direction in which the printer 1 is viewed from the front side.

An apparatus main body 2 of the printer 1 includes a sheet feeding part 3 configured to feed a sheet S, an image forming part 4 configured to form a toner image on the sheet S fed by the sheet feeding part 3, a fixing device 5 configured to fix the toner image onto the sheet S, a sheet ejection device 6 configured to eject the sheet S, and an ejected sheet tray 7 configured to receive the sheet S ejected by the sheet ejection device 6. The apparatus main body 2 also includes a conveying path 9 through which the sheet S is conveyed from the sheet feeding part 3 through the image forming part 4 and the fixing device 5 to the sheet ejection device 6.

The sheet feeding part 3 includes a cassette feeding part 11 and a manual feeding part 12 each of which is an example of the sheet feeding device. The cassette feeding part 11 is attachably/detachably provided at a lower portion of the apparatus main body 2, and the manual feeding part 12 is provided on a right side surface of the apparatus main body 2. The cassette feeding part 11 includes a sheet feeding cassette 15 on which the sheet S is stacked and a sheet feeding unit 16 configured to feed the sheet S from the sheet feeding cassette 15. The manual feeding part 12 will be described later.

The sheet S fed from the sheet feeding part 3 is conveyed along the conveying path 9. Then, the toner image is formed on the sheet S in the image forming part 4 and then fixed to the sheet S in the fixing device 5. The sheet S on which the toner image has been fixed is conveyed to the sheet ejection device 6 to be ejected onto the ejected sheet tray 7.

Next, the manual feeding part 12 will be described with reference to FIG. 1 and FIG. 2 to FIG. 5. FIG. 2 is a perspective view showing a feed roller, FIG. 3 is a perspective view showing a sheet feeding unit, FIG. 4 is a perspective view showing an upright part of the sheet feeding unit, FIG. 5 is a sectional side view showing a circumference of the feed roller, and FIG. 6 is a sectional side view showing a guide rib.

As shown in FIG. 1, the manual feeding part 12 is provided on the right side surface of the apparatus main body 2. On the right side surface of the apparatus main body 2, a sheet receiving opening 2 a and a shallow recess 2 b are formed. The sheet receiving opening 2 a is opened along a width direction perpendicular to a feeding direction of a sheet. The shallow recess 2 b is formed above the sheet receiving opening 2 a.

The manual feeding part 12 includes a feed roller 21 provided at an upper portion inside the sheet receiving opening 2 a and a sheet feeding unit 22 provided at a lower portion of the sheet receiving opening 2 a.

As shown in FIG. 2, the feed roller 21 has a pair of roller bodies 21 a and a rotation shaft 21 b. The roller bodies 21 a are provided at a center portion in the length direction of the rotation shaft 21 b with a predetermined interval.

The feed roller 21 is supported rotatably at the upper portion inside the sheet receiving opening 2 a. To a rear end portion of the rotation shaft 21 b, rotation force is transmitted from a driving source (not shown), such as a motor. The feed roller 21 is driven by the driving source to be rotated in the clockwise direction in FIG. 2.

As shown in FIG. 3, the sheet feeding unit 22 has a support member 31, a manual tray 32, a lift plate 33, two separation pads 34 and a pair of guide ribs 35 (refer to FIG. 4). The support member 31 is fixed to the lower portion of the sheet receiving opening 2 a. The manual tray 32 is supported by the support member 31 in a turnable manner. The lift plate 33 is provided on the downstream side of the manual tray 32 in the feeding direction. The two separation pads 34 are provided on the downstream side of the lift plate 33 in the feeding direction. The guide ribs 35 (refer to FIG. 4) each of which is an example of a guide part are provided on both sides of the separation pads 34 in the width direction.

The support member 31 has a base part 31 a provided along a lower edge of the sheet receiving opening 2 a and an upright part 31 b provided along a downstream side end portion of the base part 31 a.

The manual tray 32 is supported by the base part 31 a in a turnable manner upwardly and downwardly around its lower end. The manual tray 32 is a rectangular plate-like member having a stacking surface 32 a on which the sheet is stacked. The manual tray 32 is turnable between a storage position in which the manual tray 32 is turned upwardly until it is stored in the shallow recess 2 b (refer to FIG. 1) and a manual position in which the manual tray 32 is turned downwardly until it is supported in a substantially horizontal posture by a stopper (not shown).

The lift plate 33 is supported by the base part 31 a on the downstream side of the manual tray 32 in a turnable manner upwardly and downwardly around its upstream side end. The lift plate 33 is a plate-like member long in the width direction. On the lift plate 33, a leading end portion of the sheet stacked on the manual tray 32 is supported. At a downstream side edge of the lift plate 33, a plurality of guide pieces 33 a projecting to the downstream side are formed. Still further, at a center portion of the downstream side end portion of the lift plate 33, two friction pads 36 are attached with a predetermined interval.

The downstream side end portion of the lift plate 33 is turnable upwardly and downwardly by a driving mechanism (not shown). As shown in FIG. 5, when the downstream side end portion is turned upwardly by the driving mechanism until the lift plate 33 takes a substantially horizontal posture, the leading end portion of the sheet is lifted and brought into pressure contact with the roller bodies 21 a of the feed roller 21 from the lower side. When the downstream side end portion is turned downwardly, the lift plate 33 inclines obliquely downward and separates downward from the feed roller 21.

On an upper portion of the upright part 31 b of the support member 31, as shown in FIG. 4, a guide surface 38 inclined obliquely upward is formed so as to guide the sheet to the conveying path. The guide surface 38 continues in the downstream side from an upper surface of the lift plate 33 turned upwardly in the substantially horizontal posture. At a center portion of the guide surface 38 in the width direction, a separation pad storage recess 39 is formed.

The upright part 31 b is also provided with a plurality of guide grooves 41 along which the guide pieces 33 a are guided when the lift plate 33 is turned. The guide groove 41 is formed into an arc shape in a side view so as to follow a turning locus of a leading edge of the lift plate 33.

The two separation pads 34 are each made of material having a large coefficient of friction, such as rubber. As shown in FIG. 4, the two separation pads 34 are supported by a holder 43 while arranged side by side in the width direction. The holder 43 is supported by the separation pad storage recess 39 such that the two separation pads 34 take an obliquely upward posture along the guide surface 38. The holder 43 is attachable/detachable to/from the separation pad storage recess 39 so as to be easily replaced when the separation pads 34 are worn.

When the holder 43 to which the two separation pads 34 are supported is attached to the separation pad storage recess 39, the two separation pads 34 are pressed against the respective roller bodies 21 a of the feed roller 21 as shown in FIG. 5. Thereby, a separation nip N is formed between the roller bodies 21 a and the separation pads 34.

As shown in FIG. 4, the pair of guide ribs 35 is stood along the feeding direction from a lower end to near an upper end of the upright part 31 b on both sides of the separation pad storage recess 39 in the width direction. Each of the guide ribs 35 is separated outward from a center C of the support member 31 in the width direction by a predetermined distance D. The distance D is 40 mm to 60 mm, for example. A cross section of an upper end portion of the guide rib 35 in the width direction is formed into an arc shape projecting upward.

With reference to FIG. 6, the guide rib 35 will be described in detail below. FIG. 6 is a sectional side view showing the guide rib.

The guide rib 35 has, in order from the upstream side in the feeding direction, an upstream inclined part 35 a, a downstream inclined part 35 c and a parallel part 35 d. The upstream inclined part 35 a inclines gradually upward with respect to the guide surface 38 toward the downstream side. The downstream inclined part 35 c inclines moderately downward with respect to the guide surface 38 toward the downstream side from an apex part 35 b of the upstream inclined part 35 a. The parallel part 35 d is parallel with the guide surface 38.

The upstream inclined part 35 a inclines toward the separation nip N between a pressure contact position P of the lift plate 33 and the feed roller 21 and the separation nip N. The apex part 35 b projects mostly to the side of the feed roller 21 beyond an extension line L of the separation nip N. However, the roller body 21 a does not overlap with the guide rib 35, viewed from an axial direction of the feed roller 21. The downstream inclined part 35 c inclines in a direction separating from the separation nip N. The parallel part 35 d is separated from the feed roller 21 more than the separation nip N and extends substantially in parallel with the separation nip N. A tangential line T of the feed roller 21 at the pressure contact position P of the lift plate 33 and the feed roller 21 intersects with the upstream inclined part 35 a on slightly the upstream side of the apex part 35 b of the guide rib 35.

When the sheet S is fed from the manual feeding part 12 having the above described configuration, the lift plate 33 is turned upwardly such that an uppermost sheet S among the sheets stacked on the manual tray 32 comes into pressure contact with the feed roller 21. Then, as the feed roller 21 rotates, the uppermost sheet S is fed by friction with the feed roller 21. The fed sheet S abuts against the pair of guide ribs 35 on the upstream side of the separation nip N and then is guided along the pair of guide ribs 35 to be conveyed to the separation nip N.

When one sheet S is fed to the separation nip N, the sheet S is conveyed to the downstream side by the friction with the feed roller 21. In a case when a plurality of sheets is fed to the separation nip N, the separation pad 34 regulates the sheets, other than the uppermost sheet S, from being conveyed, and only the uppermost sheet S is fed by the feed roller 21.

In a case where the sheet S is a thick sheet whose stiffness is strong, the sheet S fed by the feed roller 21 is conveyed along the tangential line T and the leading edge of the sheet S abuts against the upstream inclined parts 35 a of the pair of guide ribs 35 on the upstream side of the separation nip N. Then, the sheet S is guided to the separation nip N along the pair of guide ribs 35 so that the leading edge of the sheet S will not collide with the separation pad 34. In the case of the thick sheet, a plurality of sheets is hardly fed by the feed roller 21 due to its own weight and is easily separated at the separation nip N, so that the sheet S can be stably guided to the separation nip N by the pair of guide ribs 35.

Meanwhile, in a case of a thin sheet whose stiffness is weak, a plurality of sheets is relatively often fed by the feed roller 21. Due to that, if the plurality of sheets S are fed to the separation nip N along the pair of guide ribs 35, it becomes difficult to separate the sheets S one by one at the separation nip N. However, in the case of the sheet S whose stiffness weak, a center portion M in the width direction of the sheet S deflects downward between the pair of guide ribs 35, as shown in FIG. 7, due to its weak stiffness when the leading edge of the sheet S fed by the feed roller 21 abuts against the pair of guide ribs 35 on the upstream side of the separation nip N. Then, the leading edge of the deflected center portion M of the sheet S comes into contact with the separation pad 34 on the upstream side of the separation nip N between the pair of guide ribs 35, and then the sheet S is fed to the separation nip N along the separation pad 34. Then, the uppermost sheet S is separated at the separation nip N and then conveyed.

Here, because the guide ribs 35 are formed on the outer sides of the center C of the support member 31 in the width direction by the predetermined distance D, i.e., 40 mm to 60 mm, it becomes possible to make the sheet S whose stiffness is weak to be deflected adequately such that the center portion of the sheet S abuts against the separation pad 34 between the pair of guide ribs 35. Meanwhile, it becomes possible to make the sheet S whose width is narrow and whose stiffness is strong, such as an envelope, abut against the pair of guide ribs 35 on the upstream side of the separation nip N.

As described above, according to the manual feeding part 12 of the present disclosure, the thick sheet abuts against the pair of guide ribs 35 on the upstream side of the separation nip N and then is guided to the separation nip N along the pair of guide ribs 35. Meanwhile, the center portion of the thin sheet deflects downward between the pair of guide ribs 35 on the upstream side of the separation nip N, and then the thin sheet is guided to the separation nip N along the separation pad 34. Accordingly, the feed roller 21 can guide both of the thick sheet and the thin sheet stably to the separation nip N even if its diameter is reduced. It is also possible to reliably prevent the double feeding at the separation nip N.

Still further, the guide ribs 35 are formed on the outer sides of the center of the support member 31 in the width direction by the distance of 40 mm to 60 mm. Accordingly, it is possible to adequately deflect the center portion of the thin sheet S and to make the sheet whose width is narrow and whose stiffness is weak, such as an envelope, come into contact with the pair of guide ribs 35.

Although the embodiment shows a case in which the present disclosure is applied to the manual feeding part 12, the present disclosure may be applied also to the cassette feeding part 11. Alternatively, the present disclosure is also applicable to a sheet feeding part of a document feeder.

While the preferable embodiment and its modified example of the image forming apparatus of the present disclosure have been described above and various technically preferable configurations have been illustrated, a technical range of the disclosure is not to be restricted by the description and illustration of the embodiment. Further, the components in the embodiment of the disclosure may be suitably replaced with other components, or variously combined with the other components. The claims are not restricted by the description of the embodiment of the disclosure as mentioned above. 

1. A sheet feeding device comprising: a feed roller configured to feed a sheet by being rotated while coming into pressure contact with the sheet; a separation pad configured to form a separation nip by being in pressure contact with the feed roller and to separate the fed sheet one by one at the separation nip; and a guide part formed along a feeding direction of the sheet on both outer sides of the feed roller in a width direction perpendicular to the feeding direction, wherein the guide part has an apex part configured to guide a leading edge of the sheet to the separation nip, the apex part projecting in a direction closer to the feed roller than an extension line of the separation nip between a pressure contact position of the feed roller and the sheet and the separation nip.
 2. The sheet feeding device according to claim 1, wherein the guide part is provided on both outer sides of a center of the feed roller in the width direction by 40 mm to 60 mm.
 3. The sheet feeding device according to claim 1, wherein the guide part includes an upstream inclined part, a downstream inclined part and a parallel part in the order from an upstream side to a downstream side in the feeding direction between the pressure contact position and the separation nip, the upstream inclined part inclining toward the separation nip, the downstream inclined part inclining in a direction separating from the separation nip from the upstream inclined part, the parallel part separating from the feed roller more than the separation nip and extending substantially in parallel with the separation nip from the downstream inclined part, wherein the apex part is formed between the upstream inclined part and the downstream inclined part.
 4. The sheet feeding device according to claim 1, wherein a tangential line of the feed roller at the pressure contact position intersects with the guide part on an upstream side of the apex part in the feeding direction.
 5. The sheet feeding device according to claim 1, wherein a cross section of an upper end portion of the guide part along the width direction is formed into an arc shape projecting upward.
 6. The sheet feeding device according to claim 1, further comprising a holder configured to support the separation pad, the holder being attachable/detachable.
 7. An image forming apparatus comprising: the sheet feeding device as set forth in claim 1; and an image forming part configured to form an image on a sheet fed by the sheet feeding device. 